Implantable medical devices are used to treat patients suffering from a variety of conditions. Examples of implantable medical devices are implantable pacemakers and implantable cardioverter-defibrillators (ICDs), which are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers, when necessary. For example, a pacemaker senses an arrhythmia, i.e., a disturbance in heart rhythm, and provides appropriate electrical stimulation pulses, at a controlled rate, to selected chambers of the heart in order to correct the arrhythmia and restore the proper heart rhythm. The types of arrhythmias that may be detected and corrected by pacemakers include bradycardias, which are unusually slow heart rates, and certain tachycardias, which are unusually fast heart rates.
Implantable cardioverter-defibrillators (ICDs) also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct the abnormal heart rate. In contrast to pacemakers, however, an ICD can also provide pulses that are much stronger and less frequent. This is because ICDs are generally designed to correct fibrillations, which is a rapid, unsynchronized quivering of one or more heart chambers, and severe tachycardias, where the heartbeats are very fast but coordinated. To correct such arrhythmias, an ICD delivers a low-, moderate-, or high-energy shock to the heart.
Pacemakers and implantable defibrillator devices are preferably designed with shapes that are easily accepted by the patient's body while minimizing patient discomfort. As a result, the corners and edges of the devices are typically designed with generous radii to present a package having smoothly contoured surfaces. It is also desirable to minimize the volume occupied by the devices as well as their mass to further limit patient discomfort. As a result, the devices continue to become thinner, smaller, and lighter.
In order to perform their pacing and/or cardioverting-defibrillating functions, pacemakers and ICDs must have an energy source, e.g., at least one battery. Known high current power sources used in implantable defibrillator devices employ deep, prismatic, six-sided rectangular solid shapes in packaging of the electrode assemblies. Examples of such deep package shapes can be found in, e.g., U.S. Pat. No. 5,486,215 (Kelm et al.) and U.S. Pat. No. 6,040,082 (Haas et. al.). While these prismatic cases have proven effective for housing and electrically insulating the electrode assemblies, there are volumetric inefficiencies associated with deep prismatic cases.
One volumetric problem associated with deep prismatic cases is the excess volumetric size of the implantable medical device caused by placing these prismatic batteries within the contoured implantable medical device. As stated above, implantable medical devices are preferably designed with shapes that are easily accepted by the patient's body and which also minimize patient discomfort. Therefore, the corners and edges of the devices are typically designed with generous radii to present a package having smoothly contoured surfaces. When the deep prismatic battery is placed within the contoured implantable device, the contours of these devices do not necessarily correspond and thus the volume occupied within the implantable device cannot be optimally minimized to further effectuate patient comfort.
Another volumetric problem associated with deep prismatic cases is the excess volume within the headspace. In a typical implantable device battery the headspace houses the electrode connector tabs, feedthrough pin, insulators, and various other connection components. In typical deep battery cases, the battery case has a prismatic top and then descends downward with possibly curved sides to a bottom. Thus while deep cases could provide for slightly contoured sides it could not provide for contours all throughout the battery case. Thus as shown in FIG. 13, the battery case would have to extend above the electrode assembly to accommodate the electrode connector tabs, feedthrough pin, etc. This is volumetrically inefficient since all that technically needs to extend from the top of the electrode assembly is the electrode connector tabs and the feedthrough pin. This inefficiency is due to manufacturing limitations, which make it difficult to create several curved surfaces in deep battery cases.
Although the use of curved battery cases in implantable devices is known, they are typically found in devices requiring only low current discharge such as pacemakers as described in U.S. Pat. No. 5,549,985 and U.S. Pat. No. 5,500,026. However, these batteries used thin, flat-layered electrodes that do not package efficiently within curved cases, thus contributing to volumetric inefficiencies. Batteries with curved cases have been used in connection with the high current batteries required for, e.g., implantable defibrillator devices. However, as discussed above, the curvature of these battery cases is limited due to manufacturing limitations associated with deep cases.
For the foregoing reasons, there is a need for a contoured, low profile battery for implantable medical devices, which allows for shape flexibility in the design of the battery to match the contours of an implantable device and fit within the available device space thus providing for a reduction in the volume of the implantable device.